Screw compressor

ABSTRACT

A screw compressor has a rotatable male driving screw and a rotatable female driven screw in meshed relation in a casing for compressing a working medium passing through the casing. The crests of the teeth of the screws have grooves which communicate with internal passages in the teeth for the supply of a fluid sealing medium. The grooves gradually increase in cross section in the direction of flow of the working medium through the casing and the passages have outlets in the grooves which gradually decrease in spacing in the direction of flow of the working medium.

United States Patent [721 Inventors Boris Lazarevich Grinpress Tikhoretsky prosp. 20, kv. 20; Ivan Akimovich Sakun, Krasnoputilovskaya u1., l2, kv. 44; Jury losifovich Dimentov, Budapeshtskaya ul., 38, korp. 2, kv. 89; Moisei Fishelevich Vainshtein, Nevsky prosp, 27, kv. l5, Leningrad, USSR.

[21] Appl. No. 753,094

[22] Filed Aug. 16, 1968 [45] Patented Jan. 26, 1971 [54] SCREW COMPRESSOR 7 Claims, 10 Drawing Figs.

52 u.s.c| 100/146,

91/84 51 1m.c|.............. B30b3/04 501 FieldofSearch 100 145,

[56] References Cited UNITED STATES PATENTS 2,845,777 8/1958 Nilsson et al. 91/84X 2,849,988 9/1958 Nilsson 91/84 3,405,604 10/ l 968 Lysholm 91/84 Primary Examiner-Edward L Roberts Attorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: A screw compressor has a rotatable male driving screw and a rotatable female driven screw in meshed relation in a casing for compressing a working medium passing through the casing. The crests of the teeth of the screws have grooves which communicate with internal passages in the teeth for the supply of a fluid sealing medium. The grooves gradually increase in cross section in the direction of flow of the working medium through the casing and the passages have outlets in the grooves which gradually decrease in spacing in the direction of flow of the working medium.

PATENTEUJANZBIQ?! 3.551697,

v sum 1 BF 3 SQIREW COMPRESSOR This invention relates to rotary machines for the compression or expansion of a handled medium, for example, to screw compressors or engines with driving and idler screws known as rotors, one of said rotors being of the male type in relation to the other, in that the teeth of one of the rotors have concave surfaces, while those ofthe other rotor have convex surfaces.

There are conventionally known screw compressors having two or more rotary screws (rotors) which mesh with each other and are accommodated in the recesses of the compressor casing in such a way that between the inner wall of the easing and the crests of the rotor teeth, as well as between separate elements of the meshed rotors, there are small gaps intended merely to compensate for the deformations caused by heat or mechanical stresses. However, the presence of these gaps inevitably results in leakage of the medium being compressed from the space at higher pressure into the space at lower pressure. Owing to this phenomenon, the degree of filling of the compressor casing decreases, causing a corresponding drop in its capacity. Furthermore, additional quantities of heat are imparted to the medium being compressed by the leakage substance, which adversely affects the process of compression and causes excessive power consumption by the compressor drive.

In order to reduce the rate of interspace leakage, the side and end faces of the compressor screws are made with sealing lugs (see, for example, the West German Pat. No. 934605, class 270, 30/01 I952).

For the purpose of sealing the working elements of the compressor and removing the heat, in some compressors a sealing fluid is used which is injected into the suction space and/or into the working space of the compressor through separate holes provided in the casing, and/or into pockets at the base of the teeth through centrally-drilled passages in the rotors (see, for example, British Pat. No. 832386, class I (2), I957).

However, the employment of the sealing lugs in the conventionally known screw machines does not eliminate but merely reduces the interspace leakage of the medium being compressed.

Injection of the sealing fluid into the working space through the holes in the casing is not very effective either because the sealing medium injected through separate holes forms but local sealing zones, or is thrown off by the revolving rotors towards the periphery, without ever reaching the zone of the gaps along the theoretical lines of contact between the profiled surfaces of the meshing screws. Additionally, at the moment of sealing fluid injection through the holes in the easing, additional energy is wasted in order to counteract the dynamic head of the compressed medium caused by the effect of the centrifugal forces in the compressor. Similarly insufficiently effective is the method of gap sealing with the fluid charged through the centrally drilled passages in the rotors to the base of the teeth. In this case the injected fluid ensures gap sealing only in a limited zone of the screw contact.

It is an object of this invention to eliminate the difficulties encountered in sealing the gaps between the working elements of the compressor and to provide such a screw compressor or engine in which, despite a comparatively simple design, the leakages of the handled medium through the gaps in the working elements is minimized, while the thermodynamic process takes place under favorable conditions, without ingress of heat.

In accordance with this invention, the above-specified object is achieved by an arrangement wherein the crests of the teeth of each rotor are provided with grooves arranged along their generatrices, said grooves communicating with a passages for the supply of a liquid or gaseous sealing medium.

According to the preferable embodiment of this invention it is desirable to provide grooves in the end faces of each rotor on the discharge side, said grooves communicating with the grooves provided in the crests of the teeth of these rotors and with the passages supplying the sealing medium.

Due to the fact that the pressure and temperature difference increases following the flow of the compressed medium towards the discharge end, the quantity of the sealing medium should be increased accordingly. To do this, it is desirable to arrange the outlets of the passages supplying the sealing medium to the grooves of the tooth crests in such a way that their spacing gradually decrease in the direction of flow of the compressed medium towards the discharge end. At the same time, the cross-sectional area of the grooves proper gradually in creases in the direction of flow of the compressed medium.

In the screw compressor with the sealing lugs located on the crest of each tooth of the rotors and/or with the sealing lugs located on the end faces of the rotors on the discharge side, the above-mentioned sealing grooves are preferably located before said lugs (in the direction of screw rotation). In this case the movement of the sealing medium through the gap to be sealed acquires the nature of a vortex flow which is the most effective means of preventing the leakage of the medium being compressed.

In the screw compressor with two sealing lugs on a crest of each tooth of the male rotor, the above-mentioned sealing grooves are preferably located at the edge of the tooth, i.e., along the theoretical lines of contact of the rotary screws.

This invention provides for the employment of not only a liquid but also a gaseous medium for sealing the working elements of the compressor. This can be done by drawing off a certain proportion of the compressed gaseous medium from the discharge pipe after the compressor (or from any other ap propriate source of gas supply) and feeding said compressed gaseous medium into the sealing grooves, after precooling in a heat-exchanger, which contributes to a higher efficiency of the machine.

The specific features and advantages of this invention will appear more completely from the following description of a few typical embodiments thereof which are given by way of example with reference to the accompanying drawings, in which:

FIG. 1 is an elevation view of a screw compressor, according to this invention, with the rotary screws viewed from the discharge side;

FIG. 2 is the same compressor as viewed from above;

FIG. 3 is section taken on line III-III in FIG. 2;

FIG. 4 is section taken on line IV-IV in FIG. 1;

FIG. 5 is section taken on line V-V in FIG. I;

FIG. 6 is section taken on line VI-VI in FIG. 2;

FIG. 7 is section taken on line VII-VII in FIG. 2;

FIG. 8 is section taken on line VIII-VIII in FIG. 2;

FIG. 9 is section taken on line IX-IX in FIG. 2; and

FIG. 10 is a section showing the arrangement of the grooves in the tooth of the male rotor having two sealing lugs.

The stationary casing ll of the screw compressor accommodates a male rotary screw 2 which meshes with a female rotary screw 3. The crests of the teeth 4, 5 (FIG. 1) of each rotor have grooves 6 located along the generatrix (FIGS. 2, 3, 4, 6, 7, 8 and 9), while on the end faces of the rotors, on the discharge side, there are grooves '7 (FIGS. 1,4 and 5) communicating with each other.

The area of the cross section of the grooves 6 gradually increases towards the discharge side (FIGS. 6 and 7). The grooves 6 and 7 communicate with drilled center holes 8 (FIGS. 1, 2, 3 and 4) through the passages 9 (FIGS. 2, 3, 4, 8, 9 and 10) made in each rotor, the spacing between said passages 9 gradually decreasing in the direction of flow of the compressed medium (FIG. 2). Due to the increased cross section area of the grooves and the increased number of the passages on the discharge side of the compressor, the amount of the sealing medium which can be supplied to the leakage points also increases.

The teeth 5 of the rotor 3, similar to the teeth 4 of the rotor 22, have respective lugs 10 (FIGS. 8 and 9) located along the periphery, after the grooves 6 in the direction of rotation of the rotor. Owing to this arrangement, the sealing medium can be supplied with a certain advance in relation to the position of the rotor lug, thus ensuring a more reliable sealing. If the rotor tooth has two or more lugs 10 (FIG. 10), the grooves 6 are located in the edges of the tooth.

The principle of operation of the screw compressor or engine is generally known, for which reason it is not described herein.

The sealing medium which is either a liquid or a gas is supplied under pressure through the drilled center holes 8 of the rotors 2 and 3, and through the passages 9 into the grooves 6 and 7 from whence it flows to the places of contact of the rotating working elements (rotors), and to the places of contact between the rotating working elements and the stationary elements of the compressor (the rotors and the casing, respectively) under pressure which is produced by the means ensuring the flow of the sealing medium and by centrifugal forces.

Consequently, at all the points and places of contact of the working elements of the compressor a reliable sealing zone is produced which prevents the compressed medium from leaking from the spaces with a higher pressure into the spaces with a lower pressure. As a result, the adverse effect of these leaks causing delivery of additional heat to the handled medium in the process of its compression is eliminated. Moreover, the elimination of leaking referred to above ensures a more complete filling of the compressor, increases the output factor and reduces the specific power consumption.

The delivery of the sealing medium, according to this invention, into the space before the lugs of the rotor teeth, ensures a more effective sealing with the consumption of the sealing medium being minimized.

We claim:

1. A screw compressor comprising a casing; a driving screw and a driven screw, one being a male screw, the other a female screw, sad screws being rotatable and in mesh with each other and installed in said casing for compressing a medium as it flows through said casing; said screws having teeth with crests provided with grooves, said screws having generatrices along which said grooves are located, said screws having passages for the supply of a fluid sealing medium, said passages communicating with said grooves. v

2. A screw compressor as claimed in claim 1, in which each screw has opposite end faces respectively at an inlet side and a discharge side for the medium being compressed, the end face of each screw on the discharge side having further grooves communicating with the grooves in the crests of the teeth of said screw and with said passages for the supply of the fluid sealing medium.

3. A screw compressor as claimed in claim l, in which said passages for the supply of a fluid sealing medium to the grooves have spaced outlets with gradually decreasing spacing in the direction of flow of the medium being compressed.

4. A screw compressor as claimed in claim 1, in which said grooves in the crests of the teeth of the rotors have gradually increasing cross-sectional areas in the direction of flow of the medium being compressed.

5. A screw compressor as claimed in claim 3, in which said grooves in the crests of the teeth of the rotors have gradually increasing cross-sectional areas in the direction of flow of the medium being compressed.

6. A screw compressor as claimed in claim 1 comprising a sealing lug on the crest of each tooth of said screws, each said screw having end faces respectively at an inlet side and a discharge side for the medium being compressed, and further sealing lugs on the end faces of said screws on the discharge sides thereof, said grooves being located in said teeth before said lugs thereon in the direction of rotation of said screws.

7. A screw compressor as claimed in claim 1 comprising two sealing lugs or the crest of each tooth of said female screw, said grooves being located at opposite edges of said tooth along the theoretical lines of contact of said screws. 

1. A screw compressor comprising a casing; a driving screw and a driven screw, one being a male screw, the other a female screw, sad screws being rotatable and in mesh with each other and installed in said casing for compressing a medium as it flows through said casing; said screws having teeth with crests provided with grooves, said screws having generatrices along which said grooves are located, said screws having passages for the supply of a fluid sealing medium, said passages communicating with said grooves.
 2. A screw compressor as claimed in claim 1, in which each screw has opposite end faces respectively at an inlet side and a discharge side for the medium being compressed, the end face of each screw on the discharge side having further grooves communicating with the grooves in the crests of the teeth of said screw and with said passages for the supply of the fluid sealing medium.
 3. A screw compressor as claimed in claim 1, in which said passages for the supply of a fluid sealing medium to the grooves have spaced outlets with gradually decreasing spacing in the direction of flow of the medium being compressed.
 4. A screw compressor as claimed in claim 1, in which said grooves in the crests of the teeth of the rotors have gradually increasing cross-sectional areas in the direction of flow of the medium being compressed.
 5. A screw compressor as claimed in claim 3, in which said grooves in the crests of the teeth of the rotors have gradually increasing cross-sectional areas in the direction of flow of the medium being compressed.
 6. A screw compressor as claimed in claim 1 comprising a sealing lug on the crest of each tooth of said screws, each said screw having end faces respectively at an inlet side and a discharge side for the medium being compressed, and further sealing lugs on the end faces of said screws on the discharge sides thereof, said grooves being located in said teeth before said lugs thereon in the direction of rotation of said screws.
 7. A screw compressor as claimed in claim 1 comprising two sealing lugs or the crest of each tooth of said female screw, said grooves being located at opposite edges of said tooth along the theoretical lines of contact of said screws. 